The present invention relates to a method for installing an offshore pipeline. More particularly, the present invention relates to a method for installing a pipe-in-pipe flowline system configured to provide direct electric resistance heating along the length of an extended subsea pipeline.
Offshore hydrocarbon recovery operations are increasingly pressing into deeper water and more remote locations. Here it is very expensive to provide surface facilities and it is desirable to minimize these requirements. Often satellite wells are completed subsea and are tied to remote platforms through extended subsea pipelines as a means to reduce the production cost. Even these platforms serving as central hubs in the offshore infrastructure are provided only the minimal facilities required for collecting and partially treating the well fluids before exporting them toward onshore facilities through yet more subsea pipelines.
The subsea pipelines crucial to this infrastructure prove a weak link as they are subject to plugging with hydrates or with paraffin deposition. Both hydrates and paraffins are of limited trouble at the pressures and temperatures experienced at the producing well, but can cause serious plugging problems when cooled to lower temperatures during pipeline transport. Further, heavier crude oils may exhibit fluid viscosity problems as the oil cools. A system for direct electric pipeline heating and methods of protecting pipelines from viscosity problems, hydrate formation and paraffin deposition have been devised to keep this infrastructure operational. This protection, though, is predicated on the installation of a pipe-in-pipe flowline with features appropriate for transmitting electrical power through the pipeline so as to heat the pipeline through electrical resistance and, in some circumstances, to drive electrical devices remote from the surface facilities.
Thus, there is a clear need for installation techniques appropriate for installing such a pipe-in-pipe flowline in long lengths for deepwater subsea pipeline service.